Base editing changes a letter; prime editing rewrites a short stretch. Inserting a whole gene at a chosen site is a harder problem, and US11952571B2 - "Systems, methods, and compositions for site-specific genetic engineering using programmable addition via site-specific targeting elements (PASTE)," issued April 9, 2024 to the Massachusetts Institute of Technology (inventors Abudayyeh, Gootenberg) - claims an approach to it.
The load-bearing limitation is programmable integration of large cargo. PASTE pairs CRISPR-based targeting with a site-specific integrase (a serine integrase) that can insert large DNA sequences - whole genes - at a chosen genomic location. The claim's novelty is the combination that achieves site-specific large-payload insertion without relying on double-strand-break-and-repair.
The CPC profile spans the hybrid mechanism: C12N 15/111 / 15/102 (editing methods), C12N 9/1276 (reverse transcriptase, the prime-editing component used to install the integrase landing site), C12N 9/22 (Cas targeting), and C12N 15/85 (the integration machinery). That cross-class signature reflects a multi-component system, not a single enzyme.
Why does cargo size define a distinct claim? Because the small-edit modalities cannot insert a functional gene - they were never built for it. A method that programmably integrates large sequences addresses a different therapeutic problem: replacing or adding an entire gene, relevant where a disease needs a working copy rather than a corrected letter. The claim reaches that large-cargo capability specifically.
For the landscape, PASTE marks a new tier above base and prime editing in the editing-modality hierarchy - integration of large payloads at defined sites. Freedom-to-operate for any whole-gene-insertion program has to consider this integrase-plus-CRISPR layer separately from the cutting, base-editing, and prime-editing estates, because it solves a problem none of those does.